The use of time values in software and hardware applications is common. For example, in some applications it may be desirable to securely calculate the “current time,” or the length of time that has elapsed since a specific event in the past. It may also be desirable to factor in any possible error in those calculations, as in some applications, a high degree of precision may be required. In other cases, high precision may not be required, but it still may be valuable to know that a time or duration is guaranteed to be within certain predefined limits (even if the precision is on the order of minutes, hours, or days). For example, relatively low-precision (on the order of hours or even days) but secure timers are often necessary in the context of validating security certificates (such as, for example, PKI certificates). What is needed are systems, apparatuses and methods for synchronizing a clock with one or more trusted time sources and for making reliable and secure time and duration calculations within known margins of error.